1. Technical Field
This disclosure relates to delay locked loops (DLLs) and more particularly to a DLL training protocol during a change in operating voltage.
2. Description of the Related Art
Many types of devices use delay locked loops (DLLs). Typically, a DLL is used to establish and maintain a particular phase relationship with a reference clock or other signal and to provide one or more delayed versions of that reference signal. When a DLL is first powered up, the DLL may enter a training mode to acquire and lock onto the reference signal edge. In addition, in many DLLs the delay line may be set up to provide the required amount of delay for the intended application. Depending on various circuit parameters such as the particular application, the operating environment, and the like, a conventional DLL may need to be retrained at some predetermined interval to accommodate drift, etc.
Generally, the parameters that affect the delay of the DLL may change slowly, and so a conventional DLL may have a long period between retraining to save power. However, certain parameters such as operating voltage changes, for example, may cause the delay values of the DLL to change rapidly with the change in voltage and thus the long interval between retraining may be inadequate. On the other hand, retraining the DLL more frequently can be problematic because retraining the DLL consumes considerably more power than normal DLL operation, and in mobile applications power consumption is an important consideration.